1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof.
2. Description of the Related Art
Regarding carrier mobility in germanium (Ge), it is known, as described in a technical reference document, Y. J. Yang et al., Appl. Phys. Lett. vol. 91, pp. 102103-1-3, that the electron mobility decreases in the order: (111) plane>(110) plane (<−110> direction)>(100) plane>(110) plane (<00-1> direction). In addition, as described in another technical reference document, T. Low et al., IEEE Trans. Electron Devices vol. 52, pp. 2430-9, the hole mobility decreases in the order: (110) plane>(111) plane>(100) plane. It is also known that P-type and N-type Ge channel MISFETs can attain the highest mobility when the current flow is in the <110> direction.
JP-A 2007-220809 (KOKAI) proposes a high-driving-force Ge nano wire MISFET that is fabricated by oxidation and concentration method and has a cross section that is a symmetrical polygon, where four or more of the planes forming the polygon are (111) planes. This nano-wire MISFET has a (111)-plane channel in which the current flows in the highest-mobility <110> direction. However, there is a problem that this MISFET also has a (100)-plane which provides lower channel mobility than that achievable on the (111) plane.
Meanwhile, JP-A 5-226636 (KOKAI) proposes, as a method of forming a (111)-plane channel, anisotropic selective etching by use of an etching protective layer and an etching solution.
Although JP-A 5-226636 (KOKAI) discloses a technique of forming an Si (111) channel region on an Si (100) substrate by anisotropic etching with an alkaline solution, it does not disclose Ge anisotropic etching and a channel shape such as a nano-wire structure.
A manufacturing technology that simply adopts etching in a direction perpendicular to the substrate such as reactive ion etching (RIE) is not sufficient to realize fabrication of a three-dimensional MISFET such as a Ge channel MISFET, particularly an NMISFET, having a three-dimensional-structure channel such as a FinFET and a nano-wire MISFET in which the channel plane is the highest-mobility (111) plane and the current direction is the <110> direction, no matter what plane orientation the substrate has.
Because there has been no technology available for producing a single nano-wire MISFET having the above structure, as a matter of cause, there has been no technology available for offering a multi-wire structure in which MISFETs of such a type are layered.